In recent years, a computer environment which is called cloud computing and which offers computer resources (hereinafter referred to as resources) on demand in response to user's request has become widely prevalent. In a cloud computing environment, an architecture where multiple business systems of different types having various requirements (such systems will be referred to as tenants hereinafter) run, while sharing resources in a computer environment is common and such architecture is called a multi-tenant environment. In the multi-tenant environment, when a new tenant joins the environment or when a running tenant requires additional resources, it may cause a situation in which there is a lack of available resources enough to meet a resource allocation request which is made to the multi-tenant environment. In Patent Literature 1, a resource allocation method is disclosed which includes a function of adjusting the quantities of resources to be allocated in response to a resource allocation request which is made, referring to the quantities of resources or the quantities of resources used in a computer environment.